The present invention relates to the field of detecting bioluminescent emissions and, more particularly, to counting photonic emissions of an aqueous solution of bioluminescent organisms to determine toxicity levels of the solution.
Bioluminescence is a visible blue light produced either intermittently or continuously by numerous terrestrial and aquatic organisms. Many marine dinoflagellate species are able to produce bioluminescence as part of their daily physiological processes. Similarly, some marine bacteria are also bioluminescent. Since various toxicants are known to reduce the light intensity output of bioluminescent bacterial cultures, they have been used as test organisms to detect the toxicity of atmospheric samples, herbicides, and some chemicals.
Phytoplankton bioassays are effective biological tools to assess environmental contamination because they are primary producers in the food chain, and their inherent sensitivity to toxic chemicals. Phytoplankton bioassays tend to be simple, rapid, and inexpensive when compared to more complicated and involved assays that use fish or invertebrate species. Phytoplankton bioassays generally involve the enumeration of phytoplankton cells to determine stress in algal populations when exposed to a single toxicant or chemical mixtures. These assays have been successful, but tend to be labor intensive.
U.S. Pat. No. 4,950,594, "Microbiological Assay Using Bioluminescent Organism" describes a method for assaying drilling fluids for toxicity. The method consists of agitating an aqueous solution of bioluminescent organisms, Pyrocystis lunula, using a stirring rod fitted into the chuck of a variable speed motor. The rod is stirred at approximately 100 rpm to stimulate the organisms to luminesce. Bioluminescence is measured with a solid state photometer circuit as described in U.S. Pat. No. 4,689,305 which provides an output current proportional to the light detected by an integrated photodetection assembly. Since the '305 circuit operates in a current mode, the integrated photodetection assembly only detects average intensity. The circuit is not sensitive enough to detect individual photons generated by the organisms.
U.S. Pat. No. 4,563,331, "System For Measuring Bioluminescence Flash Kinetics" describes a system for detecting and measuring bioluminescent signatures of planktonic organisms. The system includes a light tight chamber in which is positioned an organism sample holder containing filtered seawater and bioluminescent organisms. Photomultiplier tubes are mounted to the light tight chamber to detect any light generated by the organisms. The organisms are stimulated to luminesce by a vacuum pump which draws the seawater through a filter from the bottom of the sample holder. Signals generated by the photomultiplier tubes in response to detecting the light emissions from the organisms are provided to Davidson multichannel analyzers.
In the operation of the '331 system, the vacuum pump draws seawater through the filter at the bottom of the sample holder. The suction causes the organism to be drawn against the inlet side of the filter, where they concentrate. This tends to damage the organisms. Moreover, light generated by organisms squeezed between other organisms is not detected by the photomultiplier tubes, and further, the amount of light they produce can be highly variable. Variations in time delays between energizing the vacuum pump and initiating data collection between experiments as a result of manual operation of the '331 system introduces a variable in the experimental results. This variable makes it difficult to relate the results of one experiment to another, negatively impacting the repeatability of experiments performed using the '331 system.
Therefore, there is a need for a bioluminescent assay system in which the bioluminescent organisms may be stimulated without being damaged, and in which the stimulus is consistent. A further need exists for a bioluminescent system which provides good repeatability between experiments.